COMPOSITIONAL ANALYSIS AND MORPHOLOGICAL RELATIONSHIPS OF AMPHIBOLES, TALC, AND OTHER MINERALS FOUND IN THE TALC DEPOSITS FROM THE GOUVERNEUR MINING DISTRICT, NEW YORK, USA

We characterized the chemical composition and morphology of minerals in rock samples and processed products from two former talc mines owned by the R. T. Vanderbilt Co. in the Gouverneur Mining District, New York. The main mineral phases within these samples are tremolite, anthophyllite, serpentine, and talc. Other minerals found with the main phases include quartz, calcite, and diopside.

Bulk analyses of the samples were performed by powder X-ray diffraction (XRD) for structural phases and by X-ray fluorescence (XRF) for bulk chemical composition. Precise compositional data of individual grains was collected by wavelength dispersive spectroscopy (WDS) using an electron microprobe. Mineral formulas were calculated from the resulting weight percent oxides. The morphology of the different mineral phases was observed with backscatter electron (BSE) images and polarized light microscopy (PLM). For the microprobe and PLM analyses, the rock samples were prepared as polished thin sections and the products were prepared as polished grain mounts.

All of the mineral phases analyzed have near end-member compositions. The compositions and morphology of the minerals do not significantly vary between the Arnold Pit and Talcville. Tremolite occurs mainly as unaltered crystals. Anthophyllite occurs with an acicular habit, and often exhibits a series of fractures perpendicular to the long axis of the crystal; we found no evidence of asbestiform anthophyllite. Talc occurs as platy crystals and as fine-grained asbestiform particles as alteration products of primarily anthophyllite. The anthophyllite – talc alteration occurs along the anthophyllite grain edges, within the fractures, and between the partings of acicular crystals. Thus non-asbestiform anthophyllite alters to asbestiform talc.